an independent cometary existence. The picture to which I wish specially to refer in connection with our subject was obtained when the instrument was directed towards the North Celestial Pole.
In this particular case the clockwork which is ordinarily employed to keep the stars acting at the same point of the plate was dispensed with. The telescope, in fact, remained fixed while the heavens rotated in obedience to the diurnal motion. Under these circumstances each star, as minute after minute passed by, produced an image on a different part of the plate; the consequence of which was that, when the picture was developed, the record which the star was found to have left was a long trail instead of a sharply defined point. As each star appeared to describe a circle in the sky around the Pole, and as, in the vicinity of the Pole, these circles were small enough to be included in the plate, this polar photograph exhibited a striking spectacle. It displayed a large number of concentric circles, or rather, I should say, of portions of circles, for the exposures having lasted for about four hours, about one-sixth of each circumference was completed during that time. The effect thus produced was that of a number of circular arcs of varying sizes, and of different degrees of brightness. A representation of this photograph is given in Fig. 8.
Most conspicuous was the trail produced by the actual Pole Star itself. It is well known, of course, that though the situation of the Pole is conveniently marked by the fortunate circumstance that a bright star happened during the present century to lie in its immediate vicinity, yet, of course, this star is not actually at the Pole, and consequently, like all the other stars, Polaris itself must be re-
